1. Field of the Invention
The present invention relates to a process for fabricating a field emitter electrode, and more particularly to a novel process for fabricating a field emitter electrode in which low bond strength of carbon nanotubes, a disadvantage exhibited in a conventional electrophoretic method, is improved.
2. Description of the Related Art
Generally, a field emission device is a light source based on electron emission in vacuum and refers to an element emitting light according to the principle by which electrons emitted from micro particles are accelerated by a strong electric field to impinge upon fluorescent materials. The above-mentioned field emission device has advantages such as excellent light emitting efficiency and capability of realizing light-weight and compactness as compared to conventional illumination light sources such as an incandescent bulb, as well as environmental friendliness due to no use of heavy metals unlike fluorescent lamps and therefore has received a great deal of attention as a next generation light source for use in a variety of illumination fields and displays.
The performance of the field emission device significantly depends on the emitter electrode's capability to emit an electric field. Recently, carbon nanotubes (CNT) have been actively used as the electron emitting material for the emitter electrode having excellent electron emission characteristics.
However, it is difficult to uniformly grow carbon nanotubes on a large area substrate, and thus a process involving purifying carbon nanotubes grown by a separate process and depositing them on the substrate is generally used. Examples of representative methods for fabricating the carbon nanotube emitter electrode include typical printing method and electrophoretic methods.
Fabricating the carbon nanotube emitter electrode by the conventional printing method is performed by coating an electrode layer on a flat-surfaced substrate, and printing paste made of carbon nanotubes and silver powder on the electrode layer. This is followed by removing resin and solvent contained in the paste through a heat treatment process and exposing a portion of carbon nanotubes from the surface of the cured layer using a tape method.
However, this method has disadvantages such as being a complicated process, and having difficulty in obtaining homogeneous dispersion of carbon nanotubes, and thereby characteristics of the field emitter electrode may be deteriorated. Further, there is another problem in obtaining sufficient physical/mechanical bonding between carbon nanotubes and lower electrode materials using known paste application processes.
Alternatively, the method for fabricating the carbon nanotube emitter electrode by electrophoresis is performed by mixing previously purified carbon nanotubes (CNT) with a dispersing agent (for example, cationic dispersing agent) in an electrolyte 14, and then applying voltage to both electrodes 16 and 17 dipped in the electrolyte 14, thereby depositing carbon nanotubes (CNT) on the substrate 11 provided on the anode 16, as shown in FIG. 1.
This method using electrophoresis can realize relatively homogeneous dispersion of carbon nanotubes and simplification of the overall process, but has a problem in that it is not suitable for an apparatus requiring a long service life due to low mechanical impact resistance resulting from weak bond strength of carbon nanotubes.